Generally, a thick film composition comprises a functional phase that imparts appropriate electrically functional properties to the composition. The functional phase comprises electrically functional powders dispersed in an organic solvent containing a polymer. These compositions will typically contain a binder, e.g., a glass frit. Such a composition is fired to burn out the polymer and solvent and to impart the electrically functional properties. However, in the case of a polymer thick film, the polymer remains as an integral part of the composition after drying and only the solvent is removed. A processing requirement may include a heat treatment such as curing as known to those skilled in the art of polymer thick film technology.
Many PTF compositions are only stable up to approximately 200° C. and therefore do not lend them to soldering as this is done at temperatures of 200 to 260° C. Further, many current PTF electrode compositions do not wet well with solder and do not possess good adhesion to the substrate after soldering.
It is therefore a primary objective of this invention to produce a PTF paste composition which can be used to form a solderable conductor that adheres to the underlying substrate after soldering and a process for forming such a conductor.